Manipulating the activity of identified neurons in brain circuits is essential for studying how they are organized and how they produce behavior. Manipulating circuit activity can also be used to treat neurological and psychiatric diseases including Parkinson's Disease, depression and epilepsy. Optogenetic tools have revolutionized our ability to manipulate neuronal activity. We propose to create a set of complementary thermogenetic tools. These have the potential to reliably provide stronger levels of activation and may be activated with less invasive stimulus delivery systems. At present, such tools are used exclusively in flies. We propose to modify these tools to optimize them for use in mammalian systems.